1. Field of the Invention
The present invention relates to a process for preparing a multimetal oxide material M of the stoichiometry IMo1VaM1bM2cM3dOn  (I)where    M1 is at least one of the elements from the group consisting of Te and Sb;    M2 is at least one of the elements from the group consisting of Nb, Ti, W, Ta and Ce;    M3 is at least one of the elements from the group consisting of Pb, Ni, Co, Bi, Pd, Ag, Pt, Cu, Au, Ga, Zn, Sn, In, Re, Ir, Sm, Sc, Y, Pr, Nd and Tb;    a is from 0.01 to 1,    b is from >0 to 1,    c is from >0 to 1,    d is from >0 to 0.5 and    n is a number which is determined by the valency and frequency of the elements other than oxygen in (I),whose X-ray diffraction pattern has reflections h, i and k whose peaks are at the diffraction angles (2θ) 22.2±0.5° (h), 27.3±0.5° (i) and 28.2±0.5° (k),            the reflection h being the one with the strongest intensity with in the X-ray diffraction pattern and having a full width at half height (FWHH) of not more than 0.5°,        the intensity Pi of the reflection i and the intensity Pk of the reflection k satisfying the relationship 0.65≦R≦0.85, where R is the intensity ratio defined by the formulaR=Pi/(Pi+Pk)and        the FWHH of the reflection i and that of the reflection k being each ≦1°,but has no reflection with the peak position 2⊖=50.0±0.3°, in which first such a multimetal oxide material M is prepared with the proviso that, in the course of the preparation of this multimetal oxide material M, no precursor multimetal oxide material of this multimetal oxide material M is washed with a liquid from the group consisting of organic acids, inorganic acids, solutions of organic acids, solutions of inorganic acids and mixtures of the abovementioned group members. The present invention also relates to the use of multimetal oxide materials M obtainable according to the invention as active material for catalysts for the heterogeneously catalyzed gas-phase partial oxidation and/or ammoxidation of saturated and/or unsaturated hydrocarbons.        
2. Discussion of the Background
Multimetal oxide materials M are known (cf. for example DE-A 10248584, DE-A 10119933 and DE-A 10118814). They are suitable as catalysts for heterogeneously catalyzed partial gas-phase oxidations and/or ammoxidations of saturated and unsaturated hydrocarbons, as described, for example, in the abovementioned publications. If propane and/or propene is used as the hydrocarbon, for example, acrolein, acrylic acid and/or acrylonitrile can be produced as target compounds. These are key intermediates which are used, for example, for the preparation of polymers which can be employed, for example, as adhesives.
The preparation of multimetal oxide materials M is carried out according to the teachings of DE-A 10248584, DE-10119933 and DE-A 10118814 in a systematic manner in which first a precursor multimetal oxide material differing from a multimetal oxide material M (this term is intended to be understood as meaning very generally multimetal oxide materials which occur along the route to a multimetal oxide material M) and whose X-ray diffraction pattern has a reflection having a secondary phase at the peak position 2⊖=50.0±0.3° is produced and this precursor multimetal oxide material is then washed with a liquid from the group consisting of organic acids, inorganic acids, solutions of organic acids, solutions of inorganic acids and mixtures of the abovementioned group members. The acidic washing of Mo- and V-containing multimetal oxide materials is recommended in JP-A 8-57319 also for activation reasons.
In a less systematic manner, multimetal oxide materials M are however also obtainable directly by producing a very intimate, preferably finely divided dry blend from sources (starting compounds) of their elemental constituents and then converting said dry blend by thermal treatment into an active multimetal oxide M without a wash to be carried out as described above being involved.
Example 11 of DE-A 19835247 and Example 6 of EP-A 895809 may be mentioned by way of example.
However, a disadvantage of such directly obtained multimetal oxide materials M is that the selectivity of the formation of the target compound is as a rule not completely satisfactory when they are used as catalysts for heterogeneously catalyzed partial gas-phase oxidations and/or ammoxidations of saturated and/or unsaturated hydrocarbons.